The present invention relates generally to hearing protective earplugs and is more particularly concerned with premolded, polymeric foam earplugs of the push-in type.
Premolded polymeric foam earplugs composed of resilient polymer foam materials such as foam rubber, polyurethane or plasticized polyvinylchloride are well known in the art. For instance, in United Kingdom Patent No. 733,542, to Hultgren, there is disclosed a push-in type earplug comprising a soft, elastic, bullet-shaped spongy body element having a stiff axially oriented stem by which to facilitate insertion and removal of the spongy body element into and from the ear canal. Hultgren also discloses the possibility of controlling the acoustic attenuation properties of his plug by varying the pore size and density of the spongy body element. A major problem generally incurred with premolded earplugs of the prior art resides in the anatomical fact that the human ear canal is quite variable in size and geometry and, as a result, a single size of a premolded prior art earplug has not been found capable of accommodating the broad range of human ear canal sizes. Thus, premolded earplugs are generally produced in several sizes which, of course, increases the complexity and cost of manufacture and is bothersome throughout the distribution chain in terms of expense and complexity of purchasing and inventory control. As in the case of many other prior art premolded plugs, the earplugs of Hultgren are also said to be produced in two or three sizes. In addition, in order to assure good attenuation performance, the Hultgren plugs, as in the case of any earplug which is provided in several sizes, should be fitted to the individual wearer by a skilled hearing protection specialist. Unlike my present invention, the bullet-shaped spongy body element of the earplug disclosed by Hultgren is not possessed of viscoelastic recovery properties.
U.S. Pat. No. 2,438,339, issued to M. J. Thomas, discloses a frusto-conically shaped earplug of the push-in type having an elongated stiff cylindrical core composed of a material such as hard rubber. This core is surrounded by a frusto-conically shaped body composed of soft expandable and contractible material such as sponge rubber. The embedded stiff core is disclosed to be coextensive with the frusto-conically shaped body; that is to say, it does not extend outside the body element and thus cannot serve as a stem by which to manipulate the plug into and from the ear canal. Rather, the sole function served by the core element in the Thomas invention is that of stiffening of the body element such that the foam body is prevented from excessive lateral bending or distortion during insertion of the plug into the ear canal. In addition, Thomas mentions nothing with respect to the recovery rate or other properties of the body element of her earplug construction.
In West German No. OS 2 325 823, to Envac Establishment, filed on May 22, 1973 and laid open on Dec. 19, 1974, there is disclosed an earplug comprising a spherical polymeric foam body element having an essentially impermeable outer surface and a stiff elongate handle extending therefrom. The foam body element can be composed of such polymeric materials as polyurethane or plasticized polyvinylchloride. As in the Hultgren and Thomas patents discussed above, this opened West German application neither discloses nor suggests a viscoelastic foam body element and the plug construction taught therein is solely of the push-in type.
In my prior U.S. Pat. Nos. 3,811,437 and Re. 29,487 there are taught certain roll down type hearing protective earplugs composed of viscoelastic polymeric foam and having a size and shape adapted to be compressed, inserted into the ear canal and therein allowed to expand to result in a comfortable and complete obturation of the ear canal. Earplugs manufactured in accordance with the aforementioned patents have met with outstanding commercial success in the marketplace due to their features of easy insertability, comfort, excellent attenuation properties and their ability to be produced in a single size while competently fitting almost the entire adult population. Nevertheless, said foam earplugs do possess certain deficiencies which mitigate against their use in certain hearing protective situations. Firstly, the earplugs of my above-identified patents are prepared for insertion by initially rolling them down between thumb and fingers, thereby to compress them to below the sizes of the ear canals into which they are to be inserted. In terms of hygiene, therefore, the user's hands should be at least relatively clean at the time of use. This is not a trivial matter because in many noisy industrial environments there are abrasive materials or harsh chemicals which can become imbedded in the earplug. These contaminants may be present on the workers' hands at the time of use of the plugs and the necessity for first cleansing the hands can be a bothersome requisite in such situations. Additionally, while the preliminary step of rolling the plugs between the fingers is, indeed, a simple physical step, hand disabled users, such as those suffering from arthritis, can find the roll-down step a near or actual impossibility.